[Feature] Init/ErrorHandler: Introduce ShouldNotAutoReport interface

[mjansenDatabay]

This PR introduces a way to mark exceptions so that they are not reported by ILIAS' global error handling, and adds documentation for the Error Handling roadmap.

Marker interface

• New interface: ILIAS\Init\ErrorHandling\Exception\ShouldNotAutoReport in components/ILIAS/Init/src/ErrorHandling/Exception/ShouldNotAutoReport.php.
• Exceptions implementing this interface are not reported: no log file is written, and nothing is written to the application log or PHP's error_log() when they are handled by Whoops' default and logging handlers.
• The user still sees an error page (by being redirected to error.php); only the reporting step is skipped.
• Use this for expected or high-volume exceptions (e.g. routing/dispatching failures, invalid request parameters) to avoid log noise and unnecessary I/O.

ilErrorHandling

• defaultHandler() (for production env.): if the exception implements the new interface, no log file is written, and the user sees a generic error message instead of a "logfile has been created" message.
• loggingHandler(): if the exception implements the marker interface, it returns without writing to the app log or system logger.

Documentation

• README.md in Init/src/ErrorHandling/: describes the new marker interface, when to use it, how ilErrorHandling uses it, and a short usage example.
• ROADMAP.md: short-term goal to get rid of redirects to error.php from the default exception handler and respond in-place with the error page (one response per error instead of redirect and second request, this is related to [Improvement] Init: Introduce ErrorResponder (first usage: handle ilCtrl routing errors as HTTP 404) #11110).

Motivation

• Lets components opt out of reporting for specific exception types without touching global handler configuration.
• Reduces I/O and log volume for expected or client-side failures (e.g. bots, broken links).